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Chapter 10 - Circles. Section 10.2 – Arcs and Chords. How Do You Measure a Circle or Parts of a Circle?. Area Circumference Arc length Arc measure. Unit Goal. Use properties of arcs of circles. A. is a central angle. P. B. Central Angles.
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Chapter 10 - Circles Section 10.2 – Arcs and Chords
How Do You Measure a Circle or Parts of a Circle? • Area • Circumference • Arc length • Arc measure
Unit Goal • Use properties of arcs of circles
A is a central angle P B Central Angles • A central angle is an angle whose vertex is the center of the circle and whose sides intersect the circle.
A P B Measuring Arcs • The measure of an arc is the same as the measure of its associated central angle.
Major and Minor Arcs • A major arc is an arc whose measure is more than 180º. • A minor arc is an arc whose measure is less than 180º. • A semicircle is an arc that measures exactly 180º.
Arc Naming Minor Arcs • Minor arcs are named by their endpoints.
Arc Naming Major Arcs • Major arcs and semicircles are named by the two endpoints and a point on the arc.
a. b. c. 70º Example • Find the measure of each arc:
a. b. 90º c. 60º 40º Example • Find the measure of each arc:
Find x and : Example
Investigate on Circle C • Draw two distinct, congruent chords in circle C. • In a different color construct the central angles formed by the endpoints of your chords. • Find the measure of arc RJ and arc TK. • What do you notice?
Congruent Chord Theorem In the same circle or congruent circles, two minor arcs are congruent iff their corresponding chords are congruent.
More with Circle C • Construct line through C that is perpendicular to • Name the point of intersection A • Construct line through C that is perpendicular to • Name the point of intersection E • Measure
THEOREM In the same circle, or in congruent circles, two chords are congruent iff they are equidistant from the center.
Investigate with Circle G • Construct a diameter • Construct a chord that is perpendicular to your diameter. Name the point of concurrency K. • Determine the measures of
Theorem If one chord is a perpendicular bisector of another chord, then the first chord is a diameter. This can be used to locate a circle’s center.
Investigate on Circle E. • Draw any two chords that are not parallel to each other • Draw the perpendicular bisector of each chord. • The perpendicular bisectors should intersect at the circles center. • These are diameters.
HW Assignment TB #2